Luminescent materials and methods of preparation thereof



Feb 14 19161 T. E. slsNERos ETAL 2,971,359

LUMINESCENT MATERIALS AND METHODS OF PREPARATION THEREOF Filed June 50, 1958 INVEN T ORS 2170/1/45 E. Jin/idf BY {aai/er Z'l/lfffn/ cathode ray tubes.

United States Patent O LUMINESCENT MATERIALS AND METHODS OF PREPARATION THEREOF Thomas E. Sisneros, Gas City, and Robert T. Watson,

Marion, Ind., assignors to Radio Corporation of America, a corporation of Delaware Filed June 30, 1958, Ser. No. 745,294

11 Claims. (Cl. 117-335) particles on the support. Zinc sulfide and zinc-cadmium sulfide phosphors have long been used in this type of process for making luminescent Viewing screens for A mixture of two diierent phosphors may be used to produce a white-emitting viewing screen for television kinescopes. For example, a blueemitting zinc suliide with silver activator and a yellowemitting 'zinc-cadmium sulfide with silver activator mixed in the proper proportions produces a white-emitting material. This is referred to as a P-4 type screen.

When forming luminescent screens by settling such Vphosphors from an aqueous suspension, certain diticulties are encountered. For example, there is a tendency for the layer of settled material to be disturbed during the removal of the supernatant liquid. Also, there is relatively poor adherence to the support while the material is wet, so that Ythe material tends to avalanche if` the support is not horizontal or has areas which are in- 'clined to the horizontal, such as the curved edges of the face of the tube. The ability of the phosphor articles -toremain in place after they are settled and before drying is referred to as the wet adherence of the phosphor.`-

Subsequent to drying, the back of the luminescentl screen is aluminized. This is usually accomplished by coating the back of the phosphor layer with an organic .q lm, and then evaporating aluminum thereon. Filming --and aluminizing strains the phosphor layer, frequently causing the layer to rupture and to tear. Rupturing and` -tearing during lming and aluminizing may be avoided by improved adherence of the layer to its support. The ability of the phosphor particles to remain in place after they have been settled and dried is referred to as the dryv adherence or the lilming adherence of the material.

It is known that the wet adherence of the phosphor may be improved by coating the individual particles "thereon with calcium hydroxyphosphate.

This coating may be produced by suspending the phosphor particles in an aqueous medium containing a soluble phosphate and soluble calcium salt, adjusting the pH in the range between 10.5 and 11.0, and thenwashing and drying the phosphor particles. Subsequently, the coated phosphor particles are again suspended in an aqueous medium and f settled upon the face of the cathode ray tube or other support as described above. While such coatings are successful, nevertheless, a further improvement in the The invention relates also to 2,971,859 Patented Feb. i4, 1961 wet adherence of the phosphor is desirable. Very little has been taught as to filming adherence, and an improvement of this characteristic is also desirable.

An object of the invention is to provide luminescent materials having improved wet adherence and improved filming adherence.

A further object is to provide improved methods for treating phosphor particles to improve both the wet adherence and the filming adherence characteristic thereof.

Another object is to provide improved methods for preparing luminescent screens for cathode ray tubes.

The improved luminescent materials herein comprise finely-divided phosphor particles, each particle having a thin coating of a material selected from the group consisting of tin dioxide and zirconium dioxide. By virtue of the particular coating, the phosphor particles exhibit improved wet adherence and improved iilming adherence characteristics in subsequent screen-making processes.

The improved luminescent materials herein may be prepared by coating particles of phosphor, such as silveractivated zinc or zinc-cadmium sulde, with a thin layer of tin dioxide or zirconium dioxide. A preferred method comprises suspending the phosphor particles in an aqueous medium containing a soluble tin or zirconium salt, such as tin tetrachloride or zirconyl nitrate, adjusting the pH in the range of 2.5 to 11.0 with a soluble base, such as potassium hydroxide, and then washing and drying the phosphor particles.

The sole gure is a ow sheet chart illustrating typical steps in the improved process of the invention.

Example ].-A preferred procedure for coating blueemitting zinc sulfide particles with tin dioxide will now be described. Slurry 500 grams of the phosphor with 1500 ml. of demineralized water. A suitable blue-emitting zinc sultide is prepared by tiring an intimate mixture of 100 grams zinc sulfide, 0.011 gram silver as silver chloride, 2.0 grams magnesium chloride, 2.0 grams ammonium chloride, and 0.5 gram trisodium phosphate at about 980 C. in a covered beaker for about 45 minutes. To this slurry add in order:

(a) A solution containing 1.165 grams tin tetrachloride as the pentahydrate in ml. demineralized water. The slurry is then stirred for several minutes. (b) A solution of 0.2 N potassium hydroxide until The coatedphosphor particles are washed twice on' a filter funnel with 1000 m1. portions of demineralized water and then dried over night at 120 C. At this point, the coating has been converted from hydrated tin dioxide to tin dioxide. The dried product is sieved through 200 mesh prior to use.

The product comprises dried phosphor particles having a thin coating of tin dioxide thereon. The tin dioxide comprises about 0.1 weight percent of the weight of phosphor. The product is similar in characteristics to the conventional product except that the wet adherence is increased by about 40% and the filming adherence is increased by about 200%. The conventional product used for comparison is `silver-activated zinc sultide particles having a calcium hydroxyphosphate coating thereon.

Example 2.-A preferred procedure for coating blueemitting zinc sulfide particles with zirconium dioxide will now be described. Follow the procedure of Example 1 except substitute 1.08 grams zirconyl nitrate dihydrate for tin tetrachloride. The product comprises dry phosphor particles having a thin coating of zirconium dioxide thereon. The product is similar in characteristics to the product of Example 1. f

chloride.

'the pH change with urea. l ly-and more uniformly. throughout thesolution with urea herence=8.21/diarn.2. Vreciprocal of the hole area in square inches, the 8.21

Reagents-Any soluble tin salt such as tin nitrate, tin acetate, or tin iodide may be used in place of tin tetra- Similarly, .anysglnbleezirconium. salt, such as zirconiumsulfate, zirconiumacetate, orzirconyl.chlo ride may be used inv-place of` zirconylnitrate .dihydrate f `.Any method of obtaining .theproper pH for. precipita tion ymay be used. Sodium hydroxide, sodium carbonate,

urea, calcium hydroxide, and lithium hydroxide rn'aybe used in place of potassium hydroxide. Some bases are more preferable for obtaining desirablel pH. Ureaallows more uniform control of reaction-.because reaction will notvtake place locally (as with KOH) .when urea is first added. Only after the temperature is raised Ydoes The pH changes more slowyielding a `smoothercoating .of the particles. The pH may be adjusted to any value .withinthe .range of 2.5 to 11.0. A pH of. about 7.0 is convenientiand preferred.

Phosphorsf-The process is equally 4effective forcoatvbe used. Three hundred ml. of cushion is dispensed ,into each heather.

The cushion consists of 224v ml. barium acetate solution having a concentration of 8.67 grams per literin 6276 m1. water for one test run of 21 beakers. Then, 50ml. of phosphor suspension are dispensed into eachbeaker using an inverted 50 ml. pipette with a stainless steel underwater spray nozzle.

The phosphor suspension is preparedas follows: (l) for standard phosphor only, three grams of the phosphor is stirred for one minute in 100 ml. dilute potassium silicate solution and 600 ml. water; (2) for test phosphors, three grams of the phosphor is stirred for 59 Aminutes in 600 ,iml. water, and then for one additional minute after addition of 100 ml. silicate. 'Ille-phosphor is allowed to settle for 20 minutes, at which time-the beakers are transferred tothe jet impingement unit for test. l The wet adherence is tested by jet impingement. vA

stream of tap Water is squirted at the screen through the settling solution to erode a hole in the screen. The tap water passes through a .1 .2 mm. capillary tube -nozzle placedone inch abovefthe beaker platform. The water head is adjusted to Vresult in a flow nozzle of 15312 ml. ,per minute. v the erodedlholes are measured in. cm. and are averaged rate through this The diameters. of

for the three beakers run on each sample. Y

Calculatz'ons.-The hole diameteritself is asatisfactory expression of wet adherence.. However, to compare with former data, the hole diameter is converted to the Wet adherence unit by the followingmeans: Wet ad- The wet adherence unit is the being the conversion factor. The wet adherence unit, is

converted into relative wet adherence as follows: Relative Wet Adherence of the test phosphor-WA. test/WA. Std. 4.05, the relative wet adherence of the present standard being 4.05. Expressing Vthe results in terms of relative wet adherence, or adherence relative to the standard tends to eliminate small day-to-day test fluctuations.

Filming adherence test2-A luminescent screen is prepared by settling from an aqueous medium upon the face plate of a 21 90 bulb. A cushion, consisting of 770 cc. a solution containing 8.67 :grams barium acetate per .liter and 17,000 cc.- cold demineralized water Vis dispensed into the bulb on a pouroff table.

Next, a silicate solution, consisting of 1145 ce. dilute potassium silicate- Aand 1000 cc. water, is dispensed through a funnel and metal composite nozzle. Exactly 5 minutes later, the phosphor lo y alized H2Ov and add to slurry.

absolutely necessary 4 suspension, consisting of 6.875 grams of phosphor in 500 cc. Water, is dispensed through a funnel and a SS-18 plastic nozzle. Settling time is 30 minutes, pouro rate subsequent to settling is 6 to 7 minutes per 180. Exactly 15 minutes after the start of pouroi, the air driers are turned on to 17 p.s.i.g. andthe screens allowed to dry. The rst spot to dry (should talle slightly' over 2 minutes) is marked and 'the'testis performed in this region. f 'Y T he dry or rflming adherenceis tested byjetimpingement. The screen is rewetted gently on the barrel rinse position. Exactly three minutes later, Water at 40 p.s.i.g. is sprayed at the test area on the screen through a 0 deflection one gallon per minute nozzle (Spraying Systems Co., No. 0010). The timing of this water spray is 3 seconds on, 2 seconds oli, for a total of four times.

. TheM diametersof the erodedgholesr. are measured in cm.,

averaged, and reported as fllmina adherence?.

i EXAMPLES OF COATING PROCEDURES USED 1.01% SnO2-urea precipitation methodV (l) Slu`rrry g. of cl'lloride-freeV phosphor Ywithl 300 ml. demineralized H2O. 2) A dd 1 ml. of SnCl.,l solution g. o f SnCLySHgO per ml. Y(3) Adjust pl-I to 2.0 or below. with l -IC1 (this is not but gives moreuniform resul ts by redissolving any precipitated material and giving uniform startingV point) (4)l Dissolve 10I gfmof: urea in 25; i ml.` y' deiniiie'rliized 'H2O and add to slurry.

` '(5).'Stir and boiluntil is above6t0. y (6) Filter and wash with demineralized H2O until chloride -free (7) Dry/ overnight in 12 0 C. oven.

n. 1% snm-KOH precipitation mefhbd (1) Slurry 100 g. of chloride-free phosphor with 300 ml. demineralized H2O.

V(2) Dissolve 2.33 g, of SnCLySHgO in 50 ml. deminer- (3) A dl K OH to raise pH to 7.0. p (4) Filter and wash with demineralized H2O until chloride-free.

(5) Dry overnight in Y120 C. oven.

Ill. SnOz--HZO precipitation method n (1) Slurry 100 gfof chloride-freephosphor Withv300 ml. demineralized H2O.

'- (2)'Y Add SnCl4 solution containing 0.233 g.; of

YSnCLfSHZO per ml. Use 1.0 m1. of this solution flor each 0.1% SnO2 desired.

(3) Dilute with dernineralized H2O until p H is above 3.5. 5 -Due to container size limitation, some of H2O may have `to be decanted before-adding fresh H2O; however, this results in loss of some unprecipitated Sn and gives lower than theoretical SnO'z concentration.

(4) Filter and wash with demineralized H2O until chloride-free. f

(5) Dry overnight in 120 C. oven.

IV. 0.1% ZrOz-KOH precipitation method (1) Slurry 100 g. of chloride-free phosphor with 300 ml. demineralized H2O. v

(2). Dissolve 0.216 g. of ZrO(NO3)22H2O in 10 ml. demineralized H2O and add to slurry.

(3) Add KOH to raise pH to 7.0. l

1(4) Filter and wash with demineralizedHzO-a total of .1 liter of H2O should give sufticient washing.

`(5) Dry overnight in 120 C. oven.

V. 0.1%ZrO2-urea precipitation Vmethod y(l) Slurry- 100 g. of chloride-free phosphorl with 300 n'iLrdemineralizedH2O.l Y

demineralized H2O and add to slurry.

(3) ,Adjust pH to 2.0 or below with HC1.

5 (4) Dissolve 10 g. of vurea in 25 ml. deminei'alized (3) Adjust the pH to 10.0 by adding KOH. H20 and 'add to slurry. 41(4) Filter and wash with demineralized H20 until (5) vStir and boil until pH is above 6.0. chloride-free.

(6) Filter and wash with 1 liter of demineralized 5 1(5) Dry overnight in a 120 C. oven.

Q7) Dry Overnight in 120. C ovm xi. 0.1% A1203 and 1% smeT-KOH precipitation method 1 VI' O1% ZrOz-Hzo precp'ta-no" method 1) Sluri'y 100 g. of washed phosphor with 300 ml. (1) Slurry 100 g. of chloride-free phosphor with 300 10 demineralized H2O. m1. demineralized H2O. (2) Dissolve 0.368 g. of Al(NO3)39I-I2O in 10 ml.

(2) Dissolve 0.216 g. of Zr0(N03)3-2H20 in l0 ml. demineralized H2O and add to slurry. demineralized H20 and add to slurry. (3) Adjust pH to 7.0 with KOH.

(3) Filter and wash with 1 liter of demineralized (4) Filter and reslurry with 300 ml. demineralized H30. 15 H50.

(4) Dry overnight in 120 C. oven. (5) Follow coating procedure for 1% Sn02.

TABLE 0F ADHERENCES Relative Filming Coating Batch Wet Adher- Coating Technique ZnS ZnCdS ZnS-l-ZnCdS Size, Adherence Grams ence Hole Size Ca hydroxy-phosphate Reference 2. 2 2. 5 Sno I. Urea i300-104 68 3. 5 1. 0 Sno C115..- 100 3.1 S1102 1275051 1,359 3. 0 0. 97 S1102 .H20 131GB. 34,500 2.8 1.0 Zroi- V. Urea i30o-iAzrU 66 3. 1 0.90 Zroi IV.KOH i300-azi 100 3.0 1.1 ZrOi-- VLHio i300-22m 3.1 1.2 T102 VII.KOH 13oo-2TiA 100 3.3 1.1 Ca. hydroxy-phosphate Reference--- 3. 3 1. 9 SnO I. Urea YU2 100 4. 4 1. 2 Sno II. KOH C1514-. 100 4.1 Sno Ii. KOH GR4E1 100 4.1 0.70 Zroi IV.KOH 22s9zr 100 4.1 0.80 Zrog IV. KoH 232iB9Zr2 60 4.1 0.80 Lisioiandsno, VIH. KOH--- 0R22 100 4.1 0.95 Mg 02) 1x CRi- 100 4.0 0. 90 Ca hydroxy-nhnanhaf Reference 3. 0 2. 2 Sno. II. KOH C114 and CR5 200 3.9 0. s0 A1203 and S1102-- XI. KOH CR3 and CR6 200 4. 3 0.81 A1101 and SnOi- XI, KOH 0R39 and CR40 200 4. 3 0.93 sto X. KOH 0R11 and 0R12-. 200 3.6 1.o LizSiOi and Sno, VH1. KOH"- 0R22 and 0R23-- 2110 3.2 1.1 Mg(BO,)| IX CRl and CR8 200 3.0 1. 0

VII. 0.1% TOZ-KOH precipitation method What is claimed is: (1) slurry 100 g of washed phospholwlth 300 ml V1. A luminescent material comprising iinely-divided demjneralized H20 phosphor particles selected from the group consisting of (2) Add 0 233 g (0 138 ml) of TlCl4 to the slurry. zinc suldes and zinc cadmium suldes, each particle (3) Adjust pH to 7 0 by adding KOH having a thin coating of a material selected from the (4) Filter and wash with demlnerallzed H2O until 4 group consisting of tin dioxide and zirconium dioxide,

said coating being 0.001 to 2.0 Weight percent of the weight of said phosphor.

2. A luminescent material comprising finely-divided VIII. 0.5% 11125103 and 0.5% SnOz-KOH precipitation phosphor particles selected from the group consisting of method "o zinc suliides and zinc .cadmium suliides, each particle (l) slurry lo() g of Washed phosphor with 30() ml dehaving a thin coating of tin dioxide, said coating being mlnerallzed H20 0.001 to 2.0 Weight percent of the Weight of said (2) Dissoive 0.705 g. of Lici in 1o mi. demineraiized Phosphor. H2O and add to slurry. 5 3. A luminescent material comprising nely-divided (3) Add 21,4 ml of a potassium silicate Solution conphosphor particles selected from the group consisting of taining 0 0233 g SlOz/mL to the slurry zinc suldes and zinc cadmium suldes, each particle chloride free.

(5) Dry overnight in a 120 C. oven.

(4) Adjust PH to la() by adding 0 2 N KOH. having a thin coating of zirconium dioxide, said coating (5) Filler md reslurry with 300 ml demnerall-Zed being 0.001 to 2.0 weight percent of weight of said H 0. phosphor.

2 60 4. A luminescent material comprising finely-divided 6 Follow coatin rocedure for 0.5 7 S110 g p 0 2 phosphor particles selected from the group consisting of IX- 1% Mgoa): silver-activated zinc sullide and silver-activated zinc .(1) slurry 100 g. of washed phosphor with 250 m1, Cadmium suliide, each particle having a thin coating of a of 2.0 M NaBOz solution. material selected from the group consisting of tin diox- (2) Add 3,6 4 ml of 0 25 M MgCl2 solution 65 1de and zirconium dioxide, said coating being 0.001 to ,(3) Filler and wash with demlneralized H20 until 2.0 weight p ercent of the weight of said phosphor.

5. A luminescent material comprising finely-divided chloride-free.

(4) Dry Overnight in a 120 C' oven silver-activated zinc suliide particles, each particle having a thin coating of tin dioxide, said coating being 0.001

X. 0.5% S102-KOH prelpllil" mefhod 70 to 2.0 weight percent of the weight of said phosphor. (1) Slurry 100 g. of Washed phOSPhOr With 300 mL 6. A luminescent 'material comprising finely-divided demineralized H20. silver-activated zinc sulde particles, each particle having v(2) Add 1-415 8- (0-943 mL) 0f sich t0 the slurrya thin coating of zirconium dioxide,v said coating being 0.001 to 2.0 weight percent of the weight of said 1 i b d f 11 tr ti t z o h re :neTaiii 0i liii irc Tv11iczieunii mio'ao. 7s phosphor.

7. A method for coating phosphor particles selected from the group consisting of zine sulfides v,and zinc cadmium suldes comprising suspending said particles in an aqueous medium containing a soluble salt of a metal selected from the group consisting of tin salts andrzirconium salts, adjusting the pH so that a hydrated dioxide Ofrsaid metal is formed Washing the phosphor particles, and then drying the washed particles, thereby p producing .phosphorY particles coated with a material selected from a group consisting of tin dioxidel and zirconium dioxide, said coating being 0.001 to 2.0 weight percent of the Weight of said phosphor.

8. A -method Vfor coating phosphor particles selected from the group consisting of zinc sulfides and-zinc cadmium suliides, -said coating being 0.001 to 2.0 Weight percent of the weight of said phosphor comprising suspending said particles in Van aqueous medium, adding a v solution of a soluble zirconium salt to said suspension, adjusting the pH of said suspension to a value in the range between 2.5 and 11.0, washing the phosphor particles and then drying the Washed particles.

9. A vmethod'for coating phosphor particles selected from the group consisting of zinc Asuldes. andziuc cadmium sulides, said coating being 0.001 to 2*.0 weight percent of the Weight of said rphosphor comprising s115- and zinc cadmium suldes with a thin layer of tin `dioxide while suspended in an aqueous medium having a pH between 2.5 land 11.0, said coating being 0.001 to 2.0 weight percentof vthe weight of said phosphor.

` .11.; In'amethodfor preparing a luminescent material, the step comprising coating individual phosphor particles' selected from the igroupl'..Consisting ffzincsuides and zinc cadmium sulfides with a thin layer of zirconium dioxide While suspended in an aqueous medium having a p-H-lzetvv'eei 2.'5"`nd"lltlfsaid'coating being 0.001 to 2.0 weight percent of the weight of said phosphor.

' References Cited in the file of this patent UNITED STATES PATENTS 2,634,217 Y lSanabria Apr. 7, 1953 2,817,599 Edwards Dec. 24, 1957 .25 2,828,217 

1. A LUMINESCENT MATERIAL COMPRISING FINELY-DIVIDED PHOSPHOR PARTICLES SELECTED FROM THE GROUP CONSISTING OF ZINC SULFIDES AND ZINC CADMIUM SULFIDES, EACH PARTICLE HAVING A THIN COATING OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF THIN DIOXIDE AND ZIRCONIUM DIOXIDE, SAID COATING BEING 0.001 TO 2.0 WEIGHT PERCENT OF THE WEIGHT OF SAID PHOSPHOR. 